High quality lubricants are fundamentally important for the proper operation of modern machines, automobiles and trucks. However, the quantity of paraffins originating directly from untreated crude oil with properties which are suitable for use in good lubricants is very low compared to the increasing demand in this sector.
Heavy oil fractions containing large amounts of linear or slightly branched paraffins must be treated in order to obtain good quality oil bases in the best possible yields, using an operation which aims to eliminate the linear or slightly branched paraffins from feeds which are then used as base stock, or as kerosine or jet fuel.
High molecular weight paraffins which are linear or very slightly branched which are present in the oils or kerosine or jet fuel result in high pour points and thus in coagulation for low temperature applications. In order to reduce the pour points, such linear paraffins which are not or are only slightly branched must be completely or partially eliminated.
This operation can be carried out by extracting with solvents such as propane or methyl ethyl ketone, termed dewaxing, with propane or methyl ethyl ketone (MEK). However, such techniques are expensive, lengthy and not always easy to carry out.
A further technique is selective cracking of the longest linear paraffin chains to form compounds with a lower molecular weight, part of which can be eliminated by distillation.
Because of their form selectivity, zeolites are among the most widely used catalysts. The idea underlying their use is that zeolite structures exist which have pore openings which allow long linear or very slightly branched paraffins to enter their micropores but which exclude branched paraffins, naphthenes and aromatic compounds. This phenomenon leads to selective cracking of linear or very slightly branched paraffins.
Zeolite based catalysts with intermediate pore sizes such as ZSM-5, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35 and ZSM-38 have been described for their use in such processes.
Processes using such zeolites (ZSM-5, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35 and ZSM-38) can produce oils by cracking feeds containing less than 50% by weight of linear or linear or very slightly branched paraffins. However, for feeds containing higher quantities of these compounds, it has become apparent that cracking them leads to the formation of large quantities of products with lower molecular weights such as butane, propane, ethane and methane, which considerably reduces the yield of desired products.